1. Technical Field
The present disclosure relates in general to a processing system, and more particularly to determining an Azimuth angle of an incident beam of a Scatterometry tool to a wafer.
2. Background Art
The use of Scatterometry in semiconductor manufacturing has grown significantly over the past several years. This technology provides the capability to conduct measurements of a wide variety of critical wafer parameters, including, e.g., critical dimensions, depths and sidewall angles.
Scatterometry is generally used for the characterization of a target with a series of periodic lines and spaces, commonly referred to as grating lines. FIG. 1 shows an illustrative example of a measurement target 300 with grating lines 310. FIG. 2 shows an incident light beam 320 (incident beam) that strikes target 300 at an angle 322 to a surface normal 323 of a target surface 324. A plane 326 containing incident beam 320 and a reflected beam 328 is usually referred to as a plane of incidence. An ideal plane of incidence 326 is normal to both target 300 surface 324 and to grating lines 310, i.e., both angles 332 and 334 are 90 degrees.
The angle between the plane containing incident beam 320 and ideal plane of incidence 326 is referred to as an Azimuth angle of incidence beam 320 to target 300, specifically, to grating lines 310 of target 300. FIG. 3 shows an illustrative Azimuth angle (α) 330 of incident beam 320 to grating lines 310 of target 300. As such, Azimuth angle 330 represents a deviation between actual plane of incidence 327 and ideal plane of incidence 326.
Conventional approaches to Scatterometry either do not pay attention to the Azimuth angles of different Scatterometry tools or simply assume that the Azimuth angles are the same for all the tools. No effort has been made to determine an Azimuth angle of an incident beam to a wafer.